The present invention relates to an apparatus for coating recorded discs with a lubricant and particularly to an apparatus for creating droplets of the lubricant.
There has been developed recently a high density recorded disc, e.g., a video disc, in which the recorded information is in the form of a surface relief pattern formed along an information track in the major surfaces of the disc. Preferably, the surface relief pattern is formed in a spiral track, which can be a groove, in the major surfaces of the disc. The disc is played back with a stylus and during playback, the disc is rotated at a relatively high speed which creates friction between the playback stylus and the disc surface. In order to reduce these frictional forces and to prevent wear of the stylus and/or the record, it is desirable to provide a layer of lubricant on the surface of the disc. The lubricant should be uniformly coated over the entire surface of the disc but should be a thin layer, preferably between 200 and 300 Angstroms in thickness, so that it does not interfere with the proper playback of the disc. A suitable lubricant is described in U.S. Pat. No. 4,275,101, Wang et al.
Because of the viscosity of the lubricant, it has been found difficult to achieve the desired thin, uniform coating of the lubricant on the disc. One technique which has been developed is to apply the lubricant in solution in heptane. The lubricant is mixed with heptane, about 0.3 part of lubricant to 100 parts of heptane. The solution is then sprayed onto the surfaces of the disc by passing the disc under a series of oscillating nozzles which apply the solution. Each side of the disc is coated separately.
In order to eliminate the use of the heptane, which is expensive, toxic, flammable and explosive, another coating technique has been developed which is described in the copending application of Brian Ernest Lock, Ser. No. 190,079, filed Sept. 23, 1980, entitles METHOD AND APPARATUS FOR COATING RECORDED DISCS WITH A LUBRICANT now U.S. Pat. No. 4,309,456, issued Jan. 5, 1982. In the coating technique shown and described in the Lock application, streams of air are passed through a layer of the lubricant in a chamber to create droplets of the lubricant in the chamber supported in the air. The lubricant droplets are carried by the flow of air through an outlet opening in the top of the chamber and through suitable pipes to nozzles which are on opposite sides of a path along which a disc is carried. As the disc passes between the nozzles, the lubricant droplets are directed against the surfaces of the disc to provide a thin coating of the lubricant on the disc.
Lubricants have been developed which are a mixture of materials which are incompatible in that they do not dissolve in each other. It has been found that the apparatus of the Lock application for forming the lubricant droplets does not work well with these incompatible lubricant mixtures. Therefore, it is desirable to have an apparatus which will satisfactorily form the lubricant droplets even if the lubricant is such a mixture.